You may be partially right, but IIRC one of the studies which found a significant decrease was specifically taking bug samples from number plates rather than windscreens because number plates have been the same shape and in the same orientation for years.

Studies using the number plates, or old cars, have shown this is not the cause.

Not to mention https://en.wikipedia.org/wiki/Windshield_phenomenon

"The research also found that modern cars, with a more aerodynamic body shape, killed more insects than boxier vintage cars"

It's still an anecdote, but I've been driving the same truck for 15 years now. It definitely feels like I don't have to clean my windshield nearly as often as I used to in the summers.

The methods they use to trap and count insects ( https://en.wikipedia.org//wiki/Malaise_trap ) have been held constant for the last several decades, yet the decline continues ( https://journals.plos.org/plosone/article?id=10.1371/journal... ).

I think it's to do with the predators that used to keep the grazers in check. They are fewer because we shot them in protection of or livestock. This lead to a swath of plant extinctions...

Looking at the massive front grill of a modern truck or SUV I very much doubt this.